ORGANIC LETTERS
A Novel Recyclable Sulfur Monoxide Transfer Reagent
2001 Vol. 3, No. 22 3565-3568
Richard S. Grainger,* Alberto Procopio, and Jonathan W. Steed† Department of Chemistry, King's College London, Strand, London WC2R 2LS, U.K.
[email protected] Received August 31, 2001
ABSTRACT
Trisulfide 2-oxide 11 has been prepared from disulfide 9 via reduction to the corresponding dithiol and subsequent trapping with thionyl chloride. Heating trisulfide oxide 11 in the presence of dienes results in transfer of sulfur monoxide to form cyclic unsaturated sulfoxides 13 in good to excellent yields, along with recovery of disulfide 9. A Pummerer reaction can be used to convert the cyclic sulfoxides into thiophenes.
The search for an effective source of sulfur monoxide has proven to be a challenging problem in organic1 and inorganic2 chemistry. Early studies on episulfoxide 13 and thiadiazepin oxide 24 established that small ring sulfoxides fragment upon heating to produce alkenes and sulfur monoxide, although attempts to trap out the SdO released with dienes gave variable yields of dihydrothiophene-oxide adduct.5 More recently, Harpp has introduced episulfoxides 3 and 4 as stable, convenient sources of sulfur monoxide.6 Upon heating in toluene, 3 and 4 were found to transfer sulfur monoxide to four different dienes in good yields. The metal complex † To whom correspondence regarding crystal structure should be addressed. (1) (a) Harpp, D. N. Phosphorus, Sulfur, Silicon 1997, 120/121, 41. (b) Tardif, S. L.; Rys, A. Z.; Abrams, C. B.; Abu-Yousef, I. A.; Leste´-Lasserre, P. B. F.; Schultz, E. K. V.; Harpp, D. N. Tetrahedron 1997, 53, 12225. (2) (a) Schenk, W. A. Angew. Chem., Int. Ed. Engl. 1987, 26, 98. (b) Huang, R.; Guzei, I. A.; Espenson, J. H. Organometallics 1999, 18, 5420. (3) (a) Dodson, R. M.; Sauers, R. J. Chem. Soc., Chem. Commun. 1967, 1189. (b) Dodson, R. M.; Nelson, J. P. J. Chem. Soc., Chem. Commun. 1969, 1159. (c) Anastassiou, A. G.; Chao, B. Y.-H. J. Chem. Soc., Chem. Commun. 1971, 979. (d) Chao, P.; Lemal, D. M. J. Am. Chem. Soc. 1973, 95, 920. (e) Lemal, D. M.; Chao, P. J. Am. Chem. Soc. 1973, 95, 922. (f) Grigg, R.; Reimer, G. J.; Wade, A. R. J. Chem. Soc., Perkin Trans. 1 1983, 1929. (4) Chow, Y. L.; Tam, J. N. S.; Blier, J. E. J. Chem. Soc., Chem. Commun. 1970, 1604. The heterocycle 2 is proposed to close to an episulfoxide prior to sulfur monoxide extrusion. (5) For transfer of sulfur monoxide from trans-2,3-diphenylethene sulfoxide to ylides, see: Bonini, B. F.; Maccagnani, G.; Mazzanti, G.; Pedrini, P.; Piccinelli, P. J. Chem. Soc., Perkin Trans. 1 1979, 1721. (6) Abu-Yousef, I. A.; Harpp, D. N. J. Org. Chem. 1997, 62, 8366.
10.1021/ol016678g CCC: $20.00 Published on Web 10/10/2001
© 2001 American Chemical Society
5, itself derived from 1, has been shown to transfer sulfur monoxide to a diene in low yield,7,8 and Simpkins has shown that rhodium-catalyzed decomposition of stilbene episulfoxide provides a means to transfer sulfur monoxide to alkenes, although this method is restricted to the highly reactive norbornene and norbornadiene.9 A recent report by Espenson described the transfer of sulfur monoxide from sultine 6, an intermediate in the methyltrioxorhenium-catalyzed oxidation of thioketones with 2 equiv of hydrogen peroxide.10 Yields of trapped adduct were limited by the incompatibility of dienes and sulfur monoxide with the strongly oxidizing conditions under which the trapping experiment was carried out.
Figure 1. Molecules used to transfer sulfur monoxide to dienes.
In searching for alternative structures that may be capable of acting as sources of sulfur monoxide, we were drawn to the unusual reactivity observed in a number of 1,8 (peri)substituted naphthalene ring systems.11 In particular, transannular interactions between two sulfur atoms in cyclic 1,8dithiasubstituted naphthalene derivatives have been extensively studied by Glass12 and Furukawa,13 and in the latter case this has led to a number of unusual photochemically mediated extrusion reactions. We chose the peri-fused trisulfide-2oxide 11 as our synthetic target.14 The synthesis of trisulfide-2-oxide 11 is shown in Scheme 1. The known disulfide 9 appeared to be an ideal precursor
Scheme 1.
provided disulfide 9 in 31% overall yield. Although the yield is only moderate, this reaction allows the rapid preparation of gram quantities of disulfide 9. The trisulfide oxide 11 is a yellow solid that can be stored refrigerated for months without decomposition. The X-ray crystal structure of 11 highlights a number of interesting structural features (Figure 2). A nonplanar
Synthesis of Trisulfide-2-oxide 11
Figure 2. X-ray crystal structure of trisulfide-2-oxide 11.
to 11, despite the somewhat laborious methods previously employed in its synthesis.15 Indeed, reduction of disulfide 9 with lithium aluminum hydride followed by reaction of the air-sensitive dithiol (10)16 with thionyl chloride in the presence of pyridine provided 11 in 65% overall yield after column chromatography.17 With our subsequent discovery that 11 does indeed act as a source of sulfur monoxide (vide infra), we developed a convenient “one-pot” synthesis disulfide 9 starting from commercially available 1-bromonaphthalene 7. Hence, lithium-halogen exchange on 7 followed by directed deprotonation18 and trapping of the resulting 1,8-dilithionaphthalene (8) with elemental sulfur19 (7) Heyke, O.; Neher, A.; Lorenz, I.-P. Z. Anorg. Allg. Chem. 1992, 23, 608. (8) For displacement of sulfur monoxide from an iridium complex and trapping with an orthoquinone, see: Schenk, W. A.; Leissner, J. Z. Naturforsch., B: Chem. Sci. 1987, 42, 799. (9) Blake, A. J.; Cooke, P. A.; Kendall, J. D.; Simpkins, N. S.; Westaway, S. M. J. Chem. Soc., Perkin Trans. 1 2000, 153. (10) Huang, R.; Espenson, J. H. J. Org. Chem. 1999, 64, 6374. (11) Balasubramaniyan, V. Chem. ReV. 1966, 66, 567. (12) Glass, R. S.; Broeker, J. L.; Firouzabadi, H. J. Org. Chem. 1990, 55, 5739. (13) For a review see: Furukawa, N. Bull. Chem. Soc. Jpn. 1997, 70, 2571. (14) For a review of trisulfides and their oxides, see: Clennan, E. L.; Stensaas, K. L. Org. Prep. Proced. Int. 1998, 30, 553 (15) (a) Zweig, A.; Hoffmann, A. K. J. Org. Chem. 1965, 30, 3997. (b) Gamage, S. A.; Smith, R. A. J. Tetrahedron 1990, 46, 2111. (16) Yui, K.; Aso, Y.; Otsubo, T.; Ogura, F. Bull. Chem. Soc. Jpn. 1988, 61, 953. (17) All compounds synthesized exhibited satisfactory spectral data (IR, 1H and 13C NMR, and MS). (18) (a) Neugebauer, W.; Clark, T.; Schleyer, P. v. R. Chem. Ber. 1983, 116, 3283. (b) Brandsma, L. PreparatiVe Polar Organometallic Chemistry; Springer-Verlag: Berlin, 1987; Vol. 1, pp 195-196. 3566
conformation is adopted by the trithiane ring, whereby the central sulfur atom S(2) lies out of the mean least-squares plane of the naphthalene ring and peri-sulfur atoms by 1.1708(14) Å (torsion angles C1-S1-S2-S3, 60.1° and C8-S3-S2-S1, 64.6°, respectively). The oxygen atom occupies a pseudoaxial position on the trithiane ring, probably as a result of stabilization of this conformer through stereoelectronic effects.20,21 Two factors point to the strain in the system. First, the enlargement of the expected bond angles at C(1), C(9), and C(8) (125.7°, 126.6°, and 124.7°) is consistent with the minimization of steric interactions associated with the close proximity of substituents at the 1,8-positions of the naphthalene ring system.11 Second, whereas S(1) is essentially coplanar with the naphthalene ring, S(3) lies 0.203(4) Å out of the mean least-squares plane, on the opposite side to S(2). The thermal stability of 11 in the absence of dienes was first investigated. Upon refluxing overnight in chlorobenzene, clean conversion to disulfide 9 was observed, along with the formation of elemental sulfur.22 Encouraged by this result, we investigated the potential of 11 to act as a source of sulfur monoxide in trapping experiments with dienes and were delighted to find that refluxing a solution of 11 in chloro(19) Meinwald, J.; Dauplaise, D.; Wudl, F.; Hauser, J. J. J. Am. Chem. Soc. 1977, 99, 255. (20) Juaristi, E.; Ordon˜ez, M. In Organosulfur Chemistry, Synthetic and Stereochemical Aspects; Page, P., Ed.; Academic Press: San Diego, CA, 1998; Vol. 2, Chapter 3, pp 63-95. (21) Pseudoaxial oxygen is also observed in other cyclic trisulfide oxide derivatives for which the X-ray crystal structures are known (all fivemembered rings): (a) Ghosh, T.; Bartlett, P. D. J. Am. Chem. Soc. 1988, 110, 7499. (b) Watson, W. H.; Krawiec, M.; Ghosh, T.; Bartlett, P. D. Acta Crystallogr. 1992, C48, 2092. (c) Kimura, T.; Hanzawa, M.; Horn, E.; Kawii, Y.; Ogawa, S.; Sato, R. Tetrahedron Lett. 1997, 38, 1607. (22) Presumed to have formed via disproportionation of sulfur monoxide to SO2 and S2O, which in turn disproportionates to SO2 and S3, a source of S8. Org. Lett., Vol. 3, No. 22, 2001
benzene with excess 2,3-dimethyl butadiene 12a resulted in quantitatiVe formation of sulfoxide 13a and disulfide 9.23 The reaction of trisulfide oxide 11 with dienes 12a-d is summarized in Table 1. Good yields of sulfoxide cycload-
Scheme 2.
Thiophene Synthesis
Table 1. Reaction of 11 with Dienes 12a-da
entry
diene
ratio 11:12
time (h)
sulfoxide/yieldb (%)
recovered 9b (%)
1 2 3 4 5 6 7
12a 12b 12c 12c 12d 12d 12d
1:10 1:10 1:2.5 1:1 1:2.5 1:1 2.5:1
14 6 6.5 3 6 6 4.5
13a/100 13b/74 13c/65 13c/50 13d/93 13d/38 13d/84
99 99 100 100 100 100 98
a
Chlorobenzene, reflux.
b
The thermal decomposition of acyclic trisulfide-2-oxides has been investigated in detail by Field and Lacefield.28,29 In contrast to 11, thermolysis of acyclic trisulfide-2-oxides gives rise to a mixture of trisulfide, disulfide, and sulfur dioxide (Scheme 3). Interestingly, the proposed mechanism
Isolated yield after column chromatography.
Scheme 3.
ducts 13 are obtained when the reaction is run with an excess of diene (entries 1-3 and 5) or an excess of 11 (entry 7). Poorer yields are obtained when a 1:1 ratio of diene to 11 is used (compare entries 3 and 4 and 5 and 6). In all cases the disulfide 9 can be easily recovered in high yield.24 Sulfoxides 13 are potentially useful intermediates in organic synthesis. For example, dehydration of the myrcenederived cycloadduct 13d under Pummerer conditions25 gave thioperillene 14, a constituent of hop and rose oil (Scheme 2).26 In the case of reaction of 11 with piperine 12e the novel thiophene 15 was isolated directly from the reaction mixture.27 (23) A slower reaction is observed in refluxing toluene; After 26 h a 65% yield of 13a was obtained. (24) Typical Experimental Procedure. Trisulfide oxide 11 and diene 12 were refluxed in degassed chlorobenzene until TLC analysis showed complete disappearance of 11. The solvent was removed under reduced pressure, and the residue was subjected to column chromatography on silica gel. The nonpolar disulfide 9 eluted first (60-80 pet-ether) followed by the sulfoxide 13 upon increasing the solvent polarity (ethanol). (25) de Lucchi, O.; Miotti, U.; Modena, G. Org. React. 1991, 40, 157. (26) (a) Elvidge, J. A.; Jones, S. P.; Peppard, T. L. J. Chem. Soc., Perkin Trans. 1 1982, 1089. (b) Araki, S.; Butsugan, Y. Bull. Chem. Soc. Jpn. 1983, 56, 1446. (c) Weyerstahl, P.; Schenk, A.; Marschall, H. Liebigs Ann. Chem. 1995, 1849. (27) Thiophene 15 could be formed via in situ dehydration of a sulfur monoxide adduct (13a), or derived from the reaction of 12e with other reactive sulfur species (ref 22). For trapping of dienes with S2O, see: (a) Ishii, A.; Nakabayashi, M.; Nakayama, J. J. Am. Chem. Soc. 1999, 121, 7959. (b) Ishii, A.; Oshida, H.; Nakayama, J. Tetrahedron Lett. 2001, 42, 3117. (c) Ishii, A.; Kawai, T.; Tekura, K.; Oshida, H.; Nakayama, J. Angew. Chem., Int. Ed. 2001, 40, 1924. Org. Lett., Vol. 3, No. 22, 2001
Thermal Decomposition of Acyclic Trisulfide-2-oxides
postulates an initial rearrangement to a disulfide-sulfur monoxide adduct 17, which rapidly reacts with a second molecule of trisulfide oxide 16. To determine whether sulfur monoxide transfer is common to all trisulfide-2-oxides, we carried out the thermal decomposition of the phenyl derivative 16 in the presence of 2,3-dimethyl butadiene 12a but did not observe the formation of any sulfoxide 13a. In summary, the novel trisulfide oxide 11 has been shown to be an effective sulfur monoxide transfer reagent in trapping experiments with dienes. The overall process benefits not only from a convenient source of sulfur monoxide in thionyl chloride but also in the generation of a recyclable byproduct (28) Field, L.; Lacefield, W. B. J. Org. Chem. 1966, 31, 3555. (29) Flash vacuum pyrolysis (>540 °C) of 1,2,3-benzotrithiole 2-oxide results in the loss of sulfur monoxide and the formation of benzodithiete: Breitenstein, M.; Schultz, R.; Schweig, A. J. Org. Chem. 1982, 47, 1979. 3567
in disulfide 9. Current efforts include elucidation of the mechanism of transfer of sulfur monoxide from 11 to dienes and application of this design principle to the generation of other reactive intermediates. Acknowledgment. We thank King’s College London for funding this work (studentship to A.P.).
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Supporting Information Available: X-ray data in CIF format for compound 11. This material is available free of charge via the Internet at http://pubs.acs.org. In addition, the author has deposited X-ray coordinates with the Cambridge Crystallographic Data Center (CCDC 171805). OL016678G
Org. Lett., Vol. 3, No. 22, 2001
